The initial set of proposed experiments is an attempt to understand the genetic mechanisms that control the sequential utilization of different globin genes during mammalian development, the phenemenon known as hemoglobin switching. The globin genes provide an excellent opportunity to examine the question of developmental regualation of gene expression because they have been intensively characterized with respect to their structure and expression. Insights into the developmental regulation of globin genes are of clinical significance because of the many hereditary disease associated with anomalous hemoglobin synthesis in man. The experimental approach to this problem involves the introduction of cloned beta globin genes into the germline of mice. The expression pattern of these genes will be analyzed in the transgenic mice and their mice and their progeny at the RNA and protein level in the various erythroid tissues during ontogeny. There are three extremely homolgous (greater than 90%) beta globin genes in goats which are descended from a common ancestral adult beta globin gene and yet they have a differential pattern of expression. Transgenic mouse lines will be generated that contain each of these beta globin genes and the expression pattern examined. From these results, hybrid genes containing portions of two different genes will be constructed and tested for expression in order to delineate what sequences play a role in the switching process. In the second project, experiments will also be performed to isolate developmental mutants which have arisen due to the insertion of foreign DNA into the mouse genome. The third project will attempt to develop a method for the elimination of B lymphocytes within the mouse. This will be carried out by introducing, into mouse eggs, a DNA fragment containing the immunoglobulin regulatory sequences which confer cell-specific expression linked to a gene whose product should kill the cell. This transgenic mouse could be used as a model system for a disease, agammaglobulinemia, in humans characterized by the inability to produce gammaglobulin. If generalized, this method could be used to make other murine analogs of human disease as well as to observe the phenotypic effects that resulted from the absence of a particular cell type.